摘要
笔者测定和解释了安徽铜陵地区赋存于中、上石炭统中的块状硫-铁-金矿床矿石铅和与成矿关系密切的闪长岩体长石铅以及该地层(围岩)全岩铅等的同位素比值及变化特征;通过这些地质体铅同位素特征的对比,提出该地区这种矿床的成矿物质来源于地层;同时通过同一矿床不同矿化类型矿石铅同位素的测定,表明不同矿化类型具有明显不同的铅同位素特征,显示出铅同位素方法利用在矿产勘探中的潜力。
The genesis and metal source of the bedded sulphur-iron-gold deposits in the Tongling District, Anhui Province, which were hosted in the Middle-Upper Carboniferous Huanglong chuanshan Formation, has long been an interesting subject for study. Pb isotopic ratios have been measured on ores of massive sulphur-iron-gold deposits occurring at Daijiachong, Mashan, Tian'ebaodanshan and Xinqiao, on feldspars from the metallization-related diorites and on whole rocks from the orehosting strata (carbonate rocks). The wariation of the measured Pb isotopic ratios is explained.
Isotopic ratios of the ore lead from those deposits lie in a field above the terrestrial lead isotope evolution line in the ^(207)Pb /^(204)Pb- ^(206)Pb/^(204)Pb digngram of Stracey's two-stage model and between 135 and 350 Ma isochrons (Fig. 1), and show that with increasing Pb concentrations ^(206)Pb/^(204)Pb ratios decrease (Fig. 2). This variation of Pb isotopic ratios was caused by the decay of the trace uranium in an open system in the ores.
The Pb isotopic features of the whole-rock samples from the ore-hosting strata (carbonate rocks) are the same as those of the ores, but the variation range of the former is wider than that of the latter (Fig. 3). The trace-uranium-corrected mean model age of the carbonates corresponds to the true age of the strata.
Pb isotopic ratios of the feldspars from the diorites lie in a field below the evolution line and between the 350 and 550 Ma isochrons(Fig. 4). The mean model age of the feldspars is older than that of the diorites and the strata. The variation range of the feldspar Pb isotopic ratios is significantly different from that of the ores (Fig.5), and it is shown that the sour- ce of the diorites was significantly depleted in uranium. When Pb isotopic data of the ores, diorites, and strata are compared, it seems quite evident that the metals in all the deposits are derived from the strata.
In addition, Pb isotopic ratios have also been measured on the colloidal pyrites wit
出处
《地质学报》
EI
CAS
CSCD
北大核心
1991年第4期347-359,共13页
Acta Geologica Sinica
